Composite mask for producing a diffuser

ABSTRACT

The invention relates to an alternative composite mask that is substantially composed of a transparent support film coated with a transparent polymer matrix that contains light-absorbing pigment particles or metal particles having an average particle size d 50  ranging between 0.5 and 10 μm.

This application is a United States National Stage Patent Applicationunder 35 U.S.C. § 371 of International Patent Application No.PCT/EP02/13846, filed Dec. 6, 2002, which claims priority to GermanPatent Application No. 101 61 200.1, filed Dec. 13, 2001.

The present invention is described in the German priority applicationNo. 10161200.1, filed Dec. 13, 2001, which is hereby incorporated byreference as is fully disclosed herein.

The present invention describes an alternative to the photomasks usedhitherto for the production of diffuser films.

According to WO 94/29768 and EP-A-0 671 638, diffuser films are producedby laminating a light-sensitive, transparent material (photo-polymer,photonanomer) onto a photographic plate (mask) and exposing thismaterial to convergent UV radiation through the latter. Thephoto-polymer or photonanomer contains monomers or nanoscale particleswhich diffuse from adjacent, unexposed areas into exposed areas of thelight-sensitive, transparent material. Materials of this type aredescribed, for example, in WO 97/38333. The mask itself consists ofphotogelatine on a glass layer and has been produced in advance by acomplex laser-writing process with subsequent wet-chemical developmentand fixing (black/white photography method). This process is verytime-consuming and expensive. The writing process and the subsequentfurther processing are susceptible to flaws (point defects), which aretransferred into the end product (diffuser). The mask material(gelatine) has very high mechanical and chemical sensitivity, whichlimits the service life of the mask. The maximum mask format that istechnically possible is currently only about 30 cm×40 cm, and continuousmasks are not available, which hinders the further conversion of thediffuser into large-area display films.

The invention therefore had the object of finding an inexpensivealternative to photomasks which can be scaled up to greater widths (forexample 0.60 m or 1.20 m) without major technical effort and arecontinuous.

The object has been achieved by a novel composite mask which consists ofa finely divided, light-absorbent pigment or finely divided metalparticles in a transparent matrix which has been applied as a thincoating to a trans-parent plastic film.

The invention therefore relates to a composite mask essentiallyconsisting of a transparent support film which has been coated with atransparent polymer matrix and light-absorbent pigment particles ormetal particles present therein having a mean particle size d₅₀ ofbetween 0.5 and 10 μm, preferably between 1 and 5 μm, particularlypreferably between 2 and 4 μm.

Suitable pigments are all finely pulverulent materials which are opaqueto the light used for diffuser production, preferably UV/VIS lighthaving a wavelength of from 190 to 500 nm. The particle size of thepigment depends on the mask structure to be produced.

Suitable pigments are inorganic and organic pigments in said particlesize. Suitable organic pigments are, for example, monoazo, disazo, lakedazo, β-naphthol, naphthol-AS, benzimidazolone, disazo condensation, azometal complex pigments and polycyclic pigments, such as, for example,phthalo-cyanine, quinacridone, perylene, perinone, thiazineindigo,thioindigo, anthanthrone, anthraquinone, flavanthrone, indanthrone,isoviolanthrone, pyranthrone, dioxazine, quinophthalone, isoindolinone,isoindoline and diketopyrrolopyrrole pigments, or carbon black pigmentsor graphite.

Suitable inorganic pigments are, for example,

-   metal oxides, such as, for example, antimony oxide, bismuth oxide,    lead oxide, cadmium oxide, chromium oxides, cobalt oxide, iron    oxides, indium oxides, copper oxides, manganese oxides, nickel    oxide, mercury oxides, titanium dioxide, zinc oxide, tin dioxides    and zirconium dioxide;-   metal sulfides, such as, for example, cadmium sulfide, molybdenum    sulfide, mercury sulfide, silver sulfide and zinc sulfide;-   metal sulfates, such as, for example, barium sulfate, calcium    sulfate, cobalt sulfate and strontium sulfate;-   metal carbonates, such as, for example, barium carbonate, lead    carbonate, calcium carbonate, strontium carbonate and zinc    carbonate;-   chromates, such as, for example, lead chromate and zinc chromate;-   and spinels of the general formula AB₂X₄, where A can be a divalent    metal, such as, for example, Fe(II), Zn, Mn, Co, Ni, Cu or Cd; B can    be a trivalent metal, such as, for example, Al, Fe(III), V, Cr or    Ti, and X can be the element O, S or Se, such as, for example,    copper chromium oxides, cobalt aluminum oxides and cobalt chromium    oxides.

Further suitable inorganic pigments are, for example, barium titanate,Berlin Blue, bismuth vanadate, chromium antimony titanium oxide,Manganese Violet, Molybdenum Blue, Molybdate Red, sulfur, titaniumnitride, ultra-marine or Tungsten Blue.

Suitable metal particles are, for example, elements such as

-   antimony, bismuth, lead, cadmium, chromium, cobalt, iron, gold,    indium, iridium, copper, magnesium, manganese, molybdenum, nickel,    osmium, palladium, platinum, rhodium, ruthenium, sarmarium,    selenium, silver, silicon, tantalum, titanium, vanadium, tungsten,    zinc, tin, zirconium or alloys, such as bronze, brass or steel.

Particular preference is given to graphite and carbon black.

The pigments and metal particles are obtained in said particle size by,for example, grinding and/or sieving of corresponding pigments, crudepigments or metal particles to the desired degree of fine division.

Suitable polymer matrix formers are preferably polymers from the groupconsisting of polyvinyl acetates, polyvinyl alcohols, polyvinylbutyrals,poly-acrylates, polymethacrylates, polyepoxides andpolyvinylpyrrolidone, which may also contain corresponding oligomersand/or monomers.

The polymer matrix may also contain conventional plastics additives,such as, for example, flow-control agents, plasticizers, preferablypolyalkylene glycols, crosslinking initiators, sensitizers, antioxidantsand solvents, such as, for example, ketones, ethers, amides, alcoholsand water.

The particularly preferred matrix material is polyvinyl alcoholdissolved in water.

The dynamic viscosity of the polymer matrix is preferably in the rangebetween 50 and 1000 mPas, in particular between 100 and 500 mPas,measured using a rotational viscometer at 25° C. and a rotational speedof 200 s⁻¹.

In order to prepare the polymer matrix, the polymer is dissolved in asolvent which is suitable for this purpose, such as, for example, water,monohydric or polyhydric alcohols, ethers and esters thereof, forexample alkanols having from 1 to 4 carbon atoms, such as, for example,methanol, ethanol, propanol, isopropanol, butanol or isobutanol;dihydric or trihydric alcohols, in particular having from 2 to 6 carbonatoms, for example ethylene glycol, propylene glycol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol,glycerol, diethylene glycol, dipropylene glycol, triethylene glycol,polyethylene glycol, tripropylene glycol and poly-propylene glycol;lower alkyl ethers of polyhydric alcohols, such as, for example,ethylene glycol monomethyl or monoethyl or monopropyl or monobutylether, ethylene glycol dimethyl or diethyl or dipropyl or dibutyl ether,diethylene glycol monomethyl or monoethyl ether, diethylene glycoldimethyl or diethyl ether, triethylene glycol monomethyl or monoethylether, triethylene glycol dimethyl or diethyl ether, propylene glycolmonomethyl or monoethyl or monopropyl or monobutyl ether, propyleneglycol dimethyl or diethyl or dipropyl or dibutyl ether, dipropyleneglycol monomethyl or mono-ethyl or monobutyl ether, dipropylene glycoldimethyl or diethyl or dibutyl ether; cyclic ethers, such astetrahydrofuran, dioxalane or dioxane; ethers, such as tert-butyl methylether or diethyl ether; ketones and ketone alcohols, such as, forexample, acetone, methyl ethyl ketone, diethyl ketone, methyl isobutylketone, methyl pentyl ketone, cyclopentanone, cyclohexanone anddiacetone alcohol; esters, such as, for example, methyl or ethyl orpropyl or butyl acetate, methyl or ethyl or propyl or butyl propanoate,butyrolactone, or methyl or ethyl lactate; amides, such as, for example,dimethylformamide, dimethylacetamide and N-methylpyrrolidone; aromaticcompounds, such as toluene or xylene; chlorinated hydrocarbons, such aschloroform or methylene chloride; acetonitrile, and mixtures thereof.

A plasticizer is preferably added to the polymer solution, increasingthe flexibility of the mask and reducing shrinkage of the matrix duringdrying so that cavities, which result in undesired light scattering,cannot form in the dried matrix material.

Particularly preferred plasticizers are diethylene glycol andpolyethylene glycols.

The pigment particles or metal particles must be homogeneously dispersedin the polymer matrix. To this end, use is made of known dispersionaids, such as, for example, dissolvers, stirrers, compounders and otherconventional dispersion units. In addition, solvents, wettingassistants, emulsifiers and dispersants, such as, for example, anionic,cationic or nonionic surfactants, can additionally be used in order toset the viscosity and surface tension of the matrix in accordance withthe requirements of the film coating method used.

The optical properties of the mask (and thus those of the diffuser to beproduced therefrom) can be adjusted via the particle size of the pigmentor metal, via the volume proportion of the pigment in the mask and viathe layer thickness of the polymer matrix.

The proportion by volume of the pigment in the matrix is preferably from0.5 to 10% by volume, in particular from 1 to 5% by volume, based on thetotal volume of the matrix including pigment or metal particle.

The layer thickness of the polymer matrix is preferably from 1 to 20 μm,in particular from 2 to 10 μm.

The support film used is a plastic film, which must be transparent tothe light used for the production of the diffuser. Preference is givento films made from polyester, cellulose acetate, polycarbonate,polypropylene, polyethylene and polymethyl methacrylate. Particularpreference is given to films made from polyethylene terephthalate.

The layer thickness of the support film is preferably from 10 to 200 μm,in particular from 20 to 150 μm, particularly preferably from 30 to 100μm.

The invention also relates to a process for the production of acomposite mask, which comprises dispersing a pigment or metal particlesof said particle size in a polymer matrix solution, coating a supportfilm with the resultant mixture, and subsequently drying the coating.

The coating of the support film can be carried out using commerciallyavailable film-coating units by the knife-coating method, preferably ata feed rate of from 0.5 to 5 m/min. The drying is advantageously carriedout at a temperature of from 60 to 150° C.

The invention also relates to the use of a composite mask for theproduction of a diffuser. To this end, the composite mask is laminatedonto a film made from a photopolymeric material, the photopolymericmaterial is exposed to convergent UV/VIS light through the compositemask in order to produce changes in the refractive index of thephotopolymeric material, causing the formation of microdomains with arefractive index graduation which correspond to the spot pattern of thecomposite mask and which are subsequently cured by UV irradiation, anddelaminating the resultant diffuser from the composite mask again. Aprocess of this type is described, for example, in EP-A-0 671 638. Thediffuser itself can be used for display films (passive waveguidesystems; increase in the viewing angle) and in architectural glass.

Preparation of a Polyvinyl Alcohol Mixture:

a) Dissolution of ®Mowiol 18-88 (Clariant): 4050 g of deionized H₂O wereintroduced into a 5 I reactor. 450 g of Mowiol 18-88 were slowly addedwith stirring (propeller stirrer, about 250 rpm). The mixture wasstirred in the reactor for about 3 days with the temperature being heldat 80° C. (reflux condenser).

b) Preparation of a PVA Mixture:

200 g of diethylene glycol and subsequently 359 g of i-PrOH were addedwith stirring (anchor stirrer, about 250 rpm) to 2000 g of the PVA (=10%of Mowiol 18-88 in water) as described in a).

Preparation of Graphite Mixture:

1.3 g of TWEEN 80 (emulsifier from Merck) were added with stirring(magnetic stirrer with magnetic bar, 300-400 rpm) to 200 g of deionizedH₂O. After dissolution of the emulsifier, 12.8 g of graphite KS 4 fromTimca were added slowly (12.8 g of graphite in about 5.30 minutes),likewise with stirring. The mixture was subsequently stirred for afurther 10 minutes and then treated with an ultrasound lance.

Production of the Graphite/Polymer Matrix:

32.5 g of graphite mixture were added with stirring (anchor stirrer,about 250 rpm) to 225 g of the PVA mixture. 37.5 g of iso-PrOH, 37.5 gof EtOH and 3.3 g of ®Byk 306 were added successively with stirring asfurther components.

Coating Process:

The graphite/polymer matrix was applied to a commercially availablepolyester film (thickness 50 μm) using a film-coating unit (Mathis,width 600 mm) by the knife-coating method at a feed rate of 2 m/min anddried at 120° C. (drying time 1.5 min) to give a composite mask.

Use of the Composite Mask:

The composite mask was laminated onto commercially availablephoto-polymer, as described, for example, in WO 94/29768, and irradiatedwith UV light (Hg lamp with cold-light mirror 350-450 nm, 2 min, 1860 ftcd) for 2 minutes in a mask aligner and subsequently fixed for 1 minuteby UV irradiation over the entire area. This gave a diffuser film(viewing angle of 16°) which has very good optical concordance comparedwith a diffuser film (viewing angle of 19°) produced by means ofconventional photomasks, as described in WO 94/29768.

In order to determine the viewing angle, the diffuser film isilluminated with convergent light from one side (perpendicular directionof incidence), and the intensity I of the transmitted light is measuredusing a photodetector as a function of the angle α. The angle α(−90°<=α<=90°) here denotes the deviation from the perpendicular. Theviewing angle corresponds to the half-value width ½. The greater theviewing angle, the greater the scattering power of the material.

1. A method for the production of a diffuser for display films andarchitectural glass, the method comprising: providing a transparentsupport film; coating the transparent support film with a transparentpolymer matrix containing light-absorbent pigment particles or metalparticles having a mean particle size d₅₀ of between 0.5 and 10 μm tothereby provide a composite mask; laminating the composite mask with aphotopolymeric material; exposing the photopolymeric material toconvergent light through the composite mask to produce a patternedphotopolymeric material having a refractive index gradient correspondingto the particles present in the composite mask; curing the patternedphotopolymeric material to provide the diffuser; and delaminating thediffuser from the composite mask.
 2. The method of claim 1, wherein thepigment particles have a mean particle size d₅₀ of between 1 and 5 μm.3. The method of claim 1, wherein the pigment particles are organicpigments.
 4. The method of claim 3, wherein the organic pigment isselected from group consisting of a monoazo, disazo, laked azo,β-naphthol, naphthol AS, benzimidazolone, disazo condensation, azo metalcomplex pigment or a phthalocyanine, quinacridone, perylene, perinone,thiazineindigo, thioindigo, anthranone, anthraquinone, flavanthrone,indanthrone, isoviolanthrone, pyranthrone, dioxazine, quinophthalone,isoindolinone, isoindoline or diketopyrrolopyrrole pigment, a carbonblack pigment or graphite.
 5. The method of claim 1, wherein the pigmentparticles are inorganic pigments.
 6. The method of claim 5, wherein theinorganic pigment is selected from the group consisting of an antimonyoxide, bismuth oxide, lead oxide, cadmium oxide, chromium oxide, cobaltoxide, iron oxide, indium oxide, copper oxide, manganese oxide, nickeloxide, mercury oxide, titanium dioxide, zinc oxide, tin dioxide,zirconium dioxide, cadmium sulfide, molybdenum sulfide, mercury sulfide,silver sulfide, zinc sulfide, barium sulfate, calcium sulfate, cobaltsulfate, strontium sulfate, barium carbonate, lead carbonate, calciumcarbonate, strontium carbonate, zinc carbonate, lead chromate, zincchromate, copper chromium oxide, cobalt aluminum oxide, cobalt chromiumoxide, barium titanate, Berlin Blue, bismuth vanadate, chromium antimonytitanium oxide, ManganeseViolet, Molybdenum Blue, Molybdate Red, sulfur,titanium nitride, ultramarine or Tungsten Blue pigment.
 7. The method ofclaim 1, wherein the metal particles are selected from the groupconsisting of antimony, bismuth, lead, cadmium, chromium, cobalt, iron,gold, indium, iridium, copper, magnesium, manganese, molybdenum, nickel,osmium, palladium, platinum, rhodium, ruthenium, samarium, selenium,silver, silicon, tantalum, titanium, vanadium, tungsten, zinc, tin,zirconium, bronze, brass or steel particles.
 8. The method of claim 1,wherein the polymer matrix is selected from the group consisting ofpolyvinyl acetate, polyvinyl alcohol, polyvinylbutyral, polyacrylate,polymethacrylate, polyepoxide, polyvinylpyrrolidone, which may alsocontain oligomers and/or monomers thereof, or a mixture thereof.
 9. Themethod of claim 1, wherein the support film is selected from the groupconsisting of polyester, cellulose acetate, polycarbonate,polypropylene, polyethylene or polymethyl methacrylate.
 10. The methodof claim 1, wherein the proportion by volume of the pigment or metalparticles in the matrix is from 0.5 to 10% by volume, based on the totalvolume of the matrix, including pigment or metal particles.
 11. Themethod of claim 1, wherein the pigment particles or metal particles havea mean particle size d₅₀ of between 2 and 4 μm.
 12. The method of claim11, wherein the pigment particles are organic pigments.
 13. The methodof claim 12, wherein the organic pigment is selected from groupconsisting of a monoazo, disazo, laked azo, β-naphthol, naphthol AS,benzimidazolone, disazo condensation, azo metal complex pigment or aphthalocyanine, quinacridone, perylene, perinone, thiazineindigo,thioindigo, anthranone, anthraquinone, flavanthrone, indanthrone,isoviolanthrone, pyranthrone, dioxazine, quinophthalone, isoindolinone,isoindoline or diketopyrrolopyrrole pigment, a carbon black pigment orgraphite.
 14. The method of claim 11, wherein the pigment particles areinorganic pigments.
 15. The method of claim 14, wherein the inorganicpigment is selected from the group consisting of an antimony oxide,bismuth oxide, lead oxide, cadmium oxide, chromium oxide, cobalt oxide,iron oxide, indium oxide, copper oxide, manganese oxide, nickel oxide,mercury oxide, titanium dioxide, zinc oxide, tin dioxide, zirconiumdioxide, cadmium sulfide, molybdenum sulfide, mercury sulfide, silversulfide, zinc sulfide, barium sulfate, calcium sulfate, cobalt sulfate,strontium sulfate, barium carbonate, lead carbonate, calcium carbonate,strontium carbonate, zinc carbonate, lead chromate, zinc chromate,copper chromium oxide, cobalt aluminum oxide, cobalt chromium oxide,barium titanate, Berlin Blue, bismuth vanadate, chromium antimonytitanium oxide, Manganese Violet, Molybdenum Blue, Molybdate Red,sulfur, titanium nitride, ultramarine or Tungsten Blue pigment.
 16. Themethod of claim 11, wherein the metal particles are selected from thegroup consisting of antimony, bismuth, lead, cadmium, chromium, cobalt,iron, gold, indium, iridium, copper, magnesium, manganese, molybdenum,nickel, osmium, palladium, platinum, rhodium, ruthenium, samariumselenium, silver, silicon, tantalum, titanium, vanadium, tungsten, zinc,tin, zirconium, bronze, brass or steel particles.
 17. The method ofclaim 11, wherein the polymer matrix is selected from the groupconsisting of polyvinyl acetate, polyvinyl alcohol, polyvinylbutyral,polyacrylate, polymethacrylate, polyepoxide, polyvinylpyrrolidone, whichmay also contain oligomers and/or monomers thereof, or a mixture thereof18. The method of claim 11, wherein the support film is selected fromthe group consisting of polyester, cellulose acetate, polycarbonate,polypropylene, polyethylene or polymethyl methacrylate.
 19. The methodof claim 11, wherein the proportion by volume of the pigment or metalparticles in the matrix is from 0.5 to 10% by volume, based on the totalvolume of the matrix, including pigment or metal particles.